Neuroanatomical, behavioral, and biochemical methods will be used to characterize the regenerating lateral olfactory tract system of the hamster. The overall purpose is to determine why the capacity to reinnervate caudal olfactory cortex is lost after the age of 7 days. Combined anatomical and behavioral experiments in individual pups will determine whether reinnervation of the olfactory tubercle correlates in time with functional recovery of olfactory guided exploration and social behavior. Small deposits of HRP will be placed in the olfactory bulb after tract section at different ages and single axons will be traced into the region of damage in order to determine if the probability of emitting long collaterals and their success in crossing the damaged region changes with age. Some cases with HRP deposits will be examined with the electronmicroscope to determine if the regenerating sprouts make specialized contacts with connective tissue elements (pia and blood vessels) and glia or whether they take any specific routes across the scar. Biochemical characterization of the tract region will determine whether the neurofilament composition changes with age and whether the stability of the neurofilaments after tract section changes after day 7. It is hoped that the results of these experiments will shed light on the cellular mechanisms responsible for functional neural remodeling both after damage and during normal development.